The present invention relates to separating certain components of a flow stream and in one aspect relates to a subsurface system for separating a portion of the gas from a gas-oil production stream, passing the separated gas through a downhole turbine-compressor unit to compress and reinject the separated gas into a downhole formation and wherein particulate material (e.g. sand) is separated from the production stream and is by-passed around the turbine to prevent damage to the turbine.
It is well known that many hydrocarbon reservoirs produce extremely large volumes of gas along with crude oil and other formation fluids, e.g. water. In producing fields such as these, it is not unusual to experience gas-to-oil ratios (GOR) as high as 25,000 standard cubic feet per barrel (scf/bbl.) or greater. As a result, large volumes of gas must be separated from the liquids before the liquids are transported for further processing, storage, and/or use. Where the production sites are near or convenient to large markets, this gas is considered a valuable asset when demands for gas are high. However, when demands are low or when a producing reservoir is located in a remote area, large volumes of produced gas can present major problems since production may have to be shut-in or at least drastically reduced if the produced gas can not be timely and properly disposed of.
In areas where substantial volumes of the produced gas can not be marketed or otherwise utilized, it is common to xe2x80x9creinjectxe2x80x9d the gas into a suitable, subterranean formation. For example, it is well known to inject the gas back into a xe2x80x9cgas capxe2x80x9d zone which often overlies a production zone of a reservoir to maintain the pressure within the reservoir and thereby increase the ultimate liquid recovery therefrom. In other applications, the gas may be injected into a producing formation through an injection well to drive the hydrocarbons ahead of the gas towards a production well. Still further, the produced gas may be injected and xe2x80x9cstoredxe2x80x9d in an appropriate, subterranean permeable formation from which it can be recovered later when the situation dictates.
To reinject the gas, large and expensive separation and compression surface facilities must be built at or near the production site. A major economic consideration in such facilities is the relatively high cost of the gas compressor train which is typically needed to compress the produced gas for reinjection. As will be understood, significant cost savings can be realized if these gas compressor requirements can be reduced.
Various methods and systems have been proposed for reducing some of the separating/handling steps normally required at the surface to process and/or re-inject at least a portion of the produced gas. These methods all basically involve the downhole separation of at least a portion of the gas from the production stream and then handling the separated gas and the remainder of the production stream separately from each other.
For example, one such method involves the positioning of an xe2x80x9caugerxe2x80x9d separator downhole within a production wellbore which separates a portion of the gas from the production stream as the stream flows upward through the wellbore; see U.S. Pat. No. 5,431,228, issued Jul. 11, 1995. The remainder of the production stream and the separated gas are then flowed to the surface through separate flowpaths where each is individually handled. While this reduces the amount of separation which would otherwise be required at the surface, the gas which is separated downhole still has to be handled at the surface.
One downhole gas separation system adapted to reduce the required surface compressor horsepower is fully disclosed and claimed in U.S. Pat. No. 5,794,697, issued Aug. 18, 1998 wherein a subsurface processing and reinjection compressor (SPARC) is positioned downhole in the wellbore. The SPARC includes an auger separator which separates a portion of the gas from the production stream and then compresses the separated gas by passing it through a turbine-driven compressor which, in turn, is driven by production stream, itself. The compressed gas is not produced to the surface but instead is injected directly into a designated formation (e.g. gas cap) within the production wellbore. For other similar downhole gas separation systems utilizing SPARCS, see U.S. Pat. Nos. 6,035,934 and 6,189,614.
Most production streams, in addition to gas, oil, and water, may contain substantial volumes of particulate material (e.g. sand). Since the production stream is also the power fluid which drives the turbine in the SPARC systems of this type, it can be seen that this entrained particulate material can cause severe erosion problems which may lead to the early failure of the SPARC. Accordingly, it is desirable to separate out as much as possible of the solid particulate material from the production stream before the stream is passed through the turbine of a SPARC.
Examples of SPARC systems which are capable of separating particulate material out of the production stream before the stream is passed through the turbine are disclosed in U.S. Pat. No. 6,026,901, issued Feb. 22, 2000 and U.S. Pat. No. 6,283,204 B1, issued Sep. 4, 2001. In these systems, liquids and particulate materials are spun outwardly as the production stream flows upward through the auger separator and are flowed upward through a spiral groove which is formed in the inner wall of the separator housing. The spiral groove empties into a passageway through the turbine housing which allows the separated particulates to bypass the turbine, itself, without passing therethrough.
The present invention is directed to this type of SPARC system wherein a substantial amount of the particulate material is separated from the production stream before the remainder of the production stream is passed through the turbine. By bypassing the separated particulate material, the erosion of the vanes of the turbine is significantly alleviated. Further, the upstream auger separator of the present invention can also be used to separate particulate and other heavy components from a flow stream at the surface.
The present invention provides a subsurface system for producing a mixed gas-oil stream to the surface from a subterranean zone through a wellbore wherein at least a portion of said gas is separated from said mixed gas-oil stream downhole and is compressed before the compressed gas is re-injected into a formation adjacent the wellbore. As will be understood in the art, the production stream will likely also include some water and some solids (e.g. sand, debris, etc.) which will be produced with the oil and gas so, as used herein, xe2x80x9cmixed gas-oil stream(s)xe2x80x9d is intended to include such production streams.
More specifically, the present system for producing d mixed gas-oil stream having liquid, gas, and solid particulates therein from a subterranean zone is comprised of a string of tubing extending from the subterranean zone to the surface. A turbine-compressor section (SPARC) is positioned in the tubing and is adapted to separate at least a portion of said liquid and said solid particulates from said gas-oil stream as said stream flows upward through said tubing. The SPARC is comprised of an upstream separator section; a turbine-compressor section; and a downstream separator section.
The upstream separator section is comprised of a housing having a first passageway(s) and a second passageway(s) through a portion thereof and which terminate in respective outlets at the upper end of the housing. A first set of slots in said inner wall of the housing near the upper end of the first auger provides an inlet for the separated liquids and solids into the first passageway(s) while a second set of slots, spaced above the first set of slots, provides an inlet into the second passageway(s). The passageways and their respective sets of slots can be formed in a liner tube which, in turn, is then positioned within the upstream separator housing.
A central support extends substantially through the housing and has a first auger flight thereon which imparts a spin to the gas-oil stream as it flows therethrough to thereby separate at least some of the liquids and some of said solids from the gas-oil stream by forcing them outward towards the inner wall of the housing by centrifugal force while leaving the remainder of said gas-oil stream to flow against said central support. A second auger flight is mounted on said central support and spaced above said first auger flight with the second set of slots being positioned between the auger flights. The second auger flight acts to xe2x80x9cdeswirlxe2x80x9d said oil-gas stream after said stream has passed through said first auger flight.
While the present upstream auger is especially useful in a downhole SPARC, it should be recognized that it can also be used at the surface to separate heavy components from a multi-component flow stream; e.g. processing a production stream after it has been produced to the surface.
The turbine-compressor section is positioned above the upstream auger separator and is comprised of a housing which has an inlet and an outlet. A shaft is journaled in the housing and has a plurality of turbine vanes affixed to one end thereof which, in turn, are positioned between the inlet and outlet of the housing. The inlet of the turbine is adapted to receive the remainder of the production stream after at least a portion of the liquids and solid particulates have been separated therefrom by the upstream separator. A bypass passage in said turbine housing fluidly connecting the outlets of the first and second passageways to the turbine outlet whereby the separated solids will bypass the turbine vanes. This substantially reduces the erosion of the turbine rotary vanes and significantly extends the operational life of the turbine.
The outlet of the bypass passage is in fluid communication with the outlet of the turbine whereby the bypass fluids and solid particulates are recombined with the remainder of the stream after the remainder of the stream has passed through the rotary turbine vanes. The recombined stream flows into the inlet of the downstream auger separator which, in turn, is comprised of a central hollow tube having an auger flight thereon. One end of the tube is fluidly connected to the inlet of the compressor which, in turn, is positioned above the turbine and is by the shaft of the turbine.
The other end of the tube has an bellmouthed inlet which allows gas that has been separated by the downstream separator to enter the tube and flow into the compressor where it is compressed before it is reinjected into a formation, e.g. gas cap, adjacent the wellbore. A deswirl auger is positioned above the gas inlet on the hollow tube to deswirl the production stream after the gas has been separated therefrom and to act as a xe2x80x9crain hatxe2x80x9d to prevent liquid from entering the gas inlet. The production stream, minus the separated gas, flows out of the downstream separator and into the production tubing through which it is then produced to the surface.